classes = {
    "":[],
    "mark":["fold","crease"],    
    "crease":["fold","crease"],    
    "valley_fold":["fold","valley"],
    "mountain_fold":["fold","mountain"],
    "xray_fold":["fold","xray"],
    "recto":["paper","edge","recto"],
    "verso":["paper","edge","verso"],
    "highlight":["paper","edge","highlight"],
    "path":["path"],
    "arrow_fold_in_front":["arrow","front"],
    "arrow_fold_backward":["arrow","backward"],
    "arrow_unfold":["arrow","unfold"],
    "arrow_fold_stretch":["arrow","front","stretch"],    
    "arrow_fold_in_front_and_unfold":["arrow","front","andunfold"],
    "arrow_fold_backward_and_unfold":["arrow","backward","andunfold"],
    "repeat_times":["arrow","symbol_arrow","repeat_times"]
}